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COVID-19

Testing

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CORONAVIRUS TESTING BASICS

This 3 minute video explains the basics of COVID-19 testing.

How to get a COVID-19 test

Understanding your test results

Order free self-test kits from COVIDtests.gov

ON THIS PAGE

COVID-19 TESTING OVERVIEW

  • There are different types of COVID-19 tests. Viral tests (NAAT and antigen) are swab or saliva tests that look for current infection. Blood tests, called antibody tests look for past infection. Only viral tests are recommended to see if you are currently infected with COVID-19.
  • Some viral tests can be done without being sent to a laboratory – this includes rapid tests, some of which can be done at home (self-tests).
  • It is important to get a COVID-19 test, even if you are up to date with your COVID-19 vaccines:
    • If you develop symptoms of COVID-19
    • If you are a close contact to someone with COVID-19
    • If you have traveled internationally or to areas in the US where COVID-19 is quickly spreading
    • As an extra layer of protection to protect others from getting sick.
    See When to get a test to learn more about when testing is required or recommended.
  • Testing is an important tool to reduce the spread of COVID-19 but testing alone is not enough. To reduce your risk, get vaccinated and boosted, wear a mask indoors, avoid crowds and spaces with poor air flow, and stay home when you are sick. Learn more at ph.lacounty.gov/reducerisk.
  • So far, it appears tests for current infection (e.g., viral tests) continue to work well at detecting COVID-19 infection with the Omicron variant.

TYPES OF COVID-19 TEST

Viral tests are swab or saliva tests.

  • They can show if you have a current infection.
  • There are two types of viral tests: antigen tests and nucleic acid amplification tests (NAATs).
  • Viral tests can be rapid tests (results in 15-30 min) or laboratory-based tests (that can take 1-3 days for results). Most antigen tests and some NAAT tests are rapid tests.
  • There are now several rapid tests that are available over-the-counter (OTC) for testing yourself at home or anywhere. Most of these are antigen tests. See self-testing to learn more.
  • PCR tests are a type of NAAT test that is usually performed in a laboratory. PCR tests are considered the most accurate test for COVID-19. They are often used to confirm the results of rapid tests.
  • NAAT and antigen tests can be used whether you have symptoms or not. There are trade-offs to both kinds of tests. Rapid tests are recommended when you need or want to know your results right away but false results are a bit more common. More accurate NAATs (usually PCR tests) are recommended to confirm some rapid test results and when a person can wait for the test result; these tests are less likely to yield a false result. Antigen tests are recommended over NAAT tests when testing to get out of isolation early or if you had COVID-19 in the past 3 months.
  • See Understanding Your Viral Test Result and What to do Next for more information.

Antibody tests (also known as serology tests) are blood tests.

  • They might tell you if you had an infection in the past, but they cannot tell you when.
  • They should not be used to test for a current infection or to tell if you are protected from getting COVID-19 in the future.
VIRAL TESTS

(swab or saliva tests)
Looks for current infection

ANTIBODY TEST

(blood tests)
Looks for past infection

NUCLEIC ACID AMPLIFICATION TEST (NAAT)
(molecular tests e.g. PCR and LAMP*)

ANTIGEN TEST

ANTIBODY TEST
(serologic test or serology)

How the test works

Detects genetic material (RNA) within the COVID-19 virus

Detects proteins (or antigens) on the surface of the COVID-19 virus

Detects antibodies made by the immune system

How the test is done

Saliva, or swab from nose or throat

Swab from nose or throat

Blood from arm or finger stick

How long it takes to get results

Same day and up to 3 days. Some are rapid (around 20 minutes)

Most are rapid, around 15 minutes or less

Same day and up to 3 days

Over the counter self-tests

A few companies make them

Many companies make them

Not available

*Includes PCR (e.g., Reverse-Transcriptase Polymerase Chain Reaction - RT-PCR) and Loop-Mediated Isothermal Amplification (LAMP)

When to Get a Test

The following information refers to COVID-19 viral tests.

  • If you have COVID-19 symptoms.
  • If you have been a "close contact" to someone with COVID-19. See ph.lacounty.gov/covidcontacts.
  • If you have COVID-19, to see if you can end isolation early. See ph.lacounty.gov/covidisolation.
  • Before and after travel. See CDC Travel for current recommendations.
  • Before or after attending a gathering or event.
  • For screening (schools, workplaces, venues, etc.).
  • If recommended by a healthcare professional or Public Health.

Note: There may be other settings that have their own testing requirements.

Understanding Your Viral Test Results and What to do Next

Talk with your doctor to make sure you understand what your viral test result means and any next steps. If you did a home test and need advice about what to do next, you can also call the DPH COVID-19 information line at 1-833-540-0473.

SUMMARY: VIRAL TESTS - WHAT A RESULT MEANS

NUCLEIC ACID AMPLIFICATION TEST (NAAT)

ANTIGEN TEST

Positive Result*

A positive result means the test found the COVID-19 virus. It is very likely you have COVID-19.
You need to follow isolation instructions.

A positive result means the test found the COVID-19 virus proteins. It is very likely you have COVID-19.

You need to follow isolation instructions.

Negative Result*

A negative result means that the virus that causes COVID-19 was not found.

A negative result means that COVID-19 virus proteins were not found.

  • If you have symptoms of COVID-19, it is recommended that you get another test a day later (antigen or NAAT) because antigen tests are more likely to miss early infections.

*No test for COVID-19 is perfect. Any test may produce:

  • False negative results
    • This means that the test result comes back negative even though you DO have COVID-19.
    • This may happen, for example, if the sample was not collected properly, the test procedure was not correctly followed, the test was taken too soon, or the test didn’t perform well.
  • False positive results
    • This means that the test result comes back positive even though you DO NOT have COVID-19.
    • This may happen, for example, if the test procedure was not followed correctly or the test didn’t perform well.

Your COVID-19 Test was POSITIVE (POS)

The test detected the COVID-19 virus. It is very likely you have COVID-19 and could spread it to others. For instructions on what to do next click on the situation that applies to you.

If you have symptoms of COVID-19

  • Isolatestay home away from others and follow instruction: ph.lacounty.gov/covidisolation.
  • Tell all of your close contacts that they have been exposed: give them the Instructions for Close Contacts available at ph.lacounty.gov/covidcontacts.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or (833) 641-0305. You can also call (833) 540-0473.
  • If you did a home/self-test and have questions about isolation or you need referrals/resources or help to notify your contacts, call the DPH COVID-19 information line at 1-833-540-0473.

Important: If you are at high risk for getting very sick from COVID-19 you may be able to get medicine to help keep you out of the hospital. Contact a doctor right away even if your symptoms are mild. Don’t delay: the medicines work best when they are given as soon as possible after symptoms start. See ph.lacounty.gov/covidmedicines for more information.

If you don’t have symptoms of COVID-19

  • Isolate- stay home away from others and follow instructions: ph.lacounty.gov/covidisolation.
  • Tell all of your close contacts that they have been exposed: give them the Instructions for Close Contacts available at ph.lacounty.gov/covidcontacts.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or (833) 641-0305. You can also call (833) 540-0473.
  • If you did a home/self-test and have questions about isolation or you need referrals/resources or help to notify your contacts, call the DPH COVID-19 information line at 1-833-540-0473.

Important: If you are at high risk for getting very sick from COVID-19 you may be able to get medicine to help keep you out of the hospital. If you develop any symptoms, even if they are very mild, contact a doctor right away. Don’t delay: the medicines work best when they are given as soon as possible after symptoms start. See ph.lacounty.gov/covidmedicines for more information.

Your COVID-19 Test was NEGATIVE (NEG)

A negative COVID-19 result means the test did NOT detect the COVID-19 virus at the time you took the test. For instructions on what to do next click on the situation that applies to you.

If you have symptoms of COVID-19

Important note: If you have been in close contact to a person with COVID-19 within the past 10 days, please follow the Instructions for Close Contacts at ph.lacounty.gov/covidcontacts.

It is possible that the test is wrong and that you are infected. This can happen if the test is taken too early or if the test misses your infection. If you continue to feel sick, keep staying away from others, and call your doctor about getting tested again.

  • If you have symptoms AND you have a negative test, stay home until at least*:
    • You have been fever-free without the help of fever-reducing medicines for at least 24 hours and
    • Your other symptoms have improved (unless your doctor told you to stay at home longer).

Note: Even with a negative test, your doctor may still diagnose you with COVID-19 based on your history, symptoms, and your physical examination (if done).

*If your negative test is an antigen test and/or an over-the-counter self-test, it is recommended that you get another test a day later (antigen or NAAT) because these tests are more likely to miss early infections.

If you are not sure what kind test you got, look at your test result report, ask your doctor, or look on the webpage where you booked the appointment.

If you don’t have symptoms of COVID-19

Important note: If you have been in close contact to a person with COVID-19 within the past 10 days, please follow Instructions for Close Contacts at ph.lacounty.gov/covidcontacts

If you are not a close contact, it is very unlikely you have COVID-19.

  • Keep safe and help prevent the spread of COVID. See Reducing Risk for information.

TESTING FOR PAST INFECTION: ANTIBODY TESTS (serology)

The basics of COVID-19 antibody testing. (1 minute video, no sound)

COVID-19 antibody tests (also known as serology tests) are blood tests that are used to look for antibodies to SARS-COV-2 (the virus that causes COVID-19). If we get COVID-19 or a COVID-19 vaccine our body’s immune system responds. It makes antibodies and prepares our immune cells to be ready to fight the virus in the future.

COVID-19 antibody tests do not look for the actual SARS-CoV-2 virus itself. They can be used to help figure out if someone was infected with COVID-19 in the past. It takes about one to three weeks after becoming infected for the body to make enough antibodies to be found by a test. Some people may take even longer, and some people who were infected with COVID-19 may never develop antibodies. NONE of the currently authorized tests are recommended to see if people have been successfully vaccinated against COVID-19.


When COVID-19 antibody tests may be useful

 There are situations where antibody tests may be helpful. For example:

  •  Doctors may order antibody tests (in addition to viral tests) for patients with a complicated illness that is difficult to diagnose.
  •  Public health organizations may use antibody tests to learn more about how the virus has spread in a community.
  •  Scientists may use antibody tests for research.

COVID-19 antibody tests cannot tell a person:

  • When or if they definitely had COVID-19
  • Whether or not they are protected (immune) from COVID-19
  • Whether it is safe to travel or spend time with other people
  • Whether they need to isolate or quarantine
  • Whether they should or should not get vaccinated
  • Whether or not their vaccine is working.

We do not know yet if having antibodies to the COVID-19 virus can protect someone from getting infected again or, if it does, how long that protection (immunity) might last. Even if you had a positive antibody test, you should continue to practice everyday prevention to protect yourself and others, including getting vaccinated. The vaccine is the best way to protect yourself from COVID-19.

Antibody tests are not 100% accurate, so false positives and negatives may occur. Talk to your doctor before being tested for antibodies. Your doctor can help you decide if you should be tested and, if you are tested, tell you what your results mean. To learn more about using antibody tests to look for past infection, visit the CDC webpage.

MORE INFORMATION

  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: webpage explains the different types of tests, and how they are performed and approved.

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Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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